As Californians stay at home, air quality improves – for now

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By Julie Cart, CalMatters | 

The global coronavirus pandemic has inadvertently achieved what state officials have sought to do for decades: Californians have parked their cars. Freeways and highways are clear. And the constant burn of fossil fuels has been markedly diminished.

The statewide stay-at-home order has brought about drastic reductions in air pollution and planet-warming emissions, experts say. The Los Angeles basin, where the term smog was invented, has enjoyed the longest period of  good air quality days since 1995, according to a UCLA researcher.

Highway traffic is down by more than half since the start of the pandemic, according to official tallies, and emissions that form smog and soot have been reduced by about the same amount in parts of the state.

For Californians with chronic health conditions, such as asthma and heart disease, the unexpected breath of fresh air is welcome.  

But to be clear, no one is celebrating. The boon to public health, coming in the midst of a public health crisis, is difficult to measure against the widespread illness and loss of life wrought by the coronavirus.

“There’s no good thing coming out of this. This is not a way we want to see a better environment,” said researcher Jordan Wildish of Earth Economics who created a dashboard tracking worldwide air quality data since the start of the pandemic. “This has been a pretty dramatic and pretty unique event.”

Significant drops in air pollution have been measured across the globe since the start of the pandemic last month, particularly in China, which toggles massive production facilities off and on, impacting worldwide emissions.

But officials caution that any environmental benefit is likely to be temporary. They expect pollution levels to ratchet back up to normal levels once isolation orders are lifted and customary economic activity resumes.

Translation: Once this is over, Californians will get back into their cars.

In the meantime, researchers are marveling at the profound change in air quality since mid-March.

Citing data aggregated by the federal Environmental Protection Agency, UCLA Fielding School of Public Health professor Yifang Zhu said average levels of tiny airborne particles known as PM2.5 dropped from about 16 micrograms per cubic meter to about 12 in the four-county Los Angeles basin after the stay at home orders. She characterized that 25% reduction as “significant.”

“We don’t need a pandemic to breathe clear air,” said Zhu.  “This should be the air we breathe every day.”

Other measurable pollutants in the area also have plummeted, according to Wildish’s dashboard: Nitrogen dioxide, which can irritate airways and trigger asthma attacks, has decreased 54%. It also is a key ingredient of ozone, the main form of smog that blankets much of California.

Other cities with well-documented pollution problems have reported similar improvement. Particulates dropped about 71% in Bakersfield in the last 10 days, while nitrogen dioxide dropped 73% in Fresno, according to Wildish’s dashboard, which is updated hourly.

California has always operated on a simple calculus: When roads are empty, skies are clearer. According to the state Department of Transportation,  “average traffic volumes from the most recent data available (Sunday, April 5) indicate traffic volumes have decreased 51% on average when compared to April 2019.”

Transportation is a perennial pollution offender, but experts warn against ascribing too much credit to reduced traffic for the clean air. Weather also is a key factor.

“There’s no doubt there has been some very clean air, but it started before the stay at home orders,” said Philip M. Fine, Deputy Executive Officer of the Planning and Rules Division for the South Coast Air Quality Management District, which regulates air pollution in Los Angeles, Orange, Riverside and San Bernardino counties, a region of 15 million residents. 

Bands of storms sweeping through the state in the last month have improved air quality dramatically, Fine said, as they always do, with the capacity to cut particulate matter and other pollutants by as much as half. 

The coronavirus erupted during breezy and rainy weather, which typically makes for good air quality.  “Weather, by far, is the biggest factor in air quality,” he said. Winter usually has the lowest levels of smog, particularly in Southern California.

Still, the role of cars and trucks in fouling the air is undeniable: About 80% of smog in California’s atmosphere comes from mobile sources, and of that, the bulk of the pollutants can be attributed to heavy duty trucks, ships and planes. 

Fine said that emissions from those sectors have dropped off  by one-fifth, tracing the same downward trajectory as the state’s economic activity.

The nexus between poor air quality and poor public health is well known, said Ed Avol, a professor at the University of Southern California who studies the impacts of air pollution in at-risk populations.
“We know that vehicle exhaust is associated with increased asthma, increased respiratory problems, it affects how well kids’ lungs grow and how they develop,” he said.

In recent weeks health officials have surmised that people with certain respiratory illnesses and other conditions linked to prolonged exposure to poor air quality are at higher risk to coronavirus.

“Air pollution impacts a body’s ability to defend itself,” Avol said. “In areas where there is more pollution, the virus has a head start. If you are exposed to it, can your body fight it off as well?”

That relationship was underscored this week as researchers at Harvard University published a study showing a statistical link between coronavirus deaths and patients with long-term exposure to pollution, especially fine particles.

Using COVID-19 death reports obtained from more than 3,000 counties across the country, the Harvard researchers overlaid local air quality data and health factors to determine pollution’s role in the patients’ deaths.

They reported that in counties with high levels of fine particulates, the increase in the death rate among people who died from the virus was 20 times higher than the rate attributed to the particles for all causes of death.

“A small increase in long-term exposure to PM2.5 leads to a large increase in COVID-19 death rate,” the authors wrote. The findings “suggest that long-term exposure to air pollution increases vulnerability to experiencing the most severe Covid-19 outcomes.”

A University of California, Berkeley group has assembled maps that show by county the highest levels of airborne particles and the rates of coronavirus cases. The highest risks were found in Kern and Kings counties in the San Joaquin Valley. is a nonprofit, nonpartisan media venture explaining California policies and politics.


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